If a player is vanished on a server using VanishNoPacket, the player count that the server reports does not change. For example, if there are two players on a server, and one of them is vanished, the server will still say something like 2/20 players, instead of 1/20 servers. This allows the ability for someone to figure out if there is a vanished player present on the server.

There is unfortunately no way to do this currently.